THE FORNIX 



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may be seen to course obliquely lateralwarcl under the splenium of the corpus cal- 

 losum. and then, continuous into the fimbria, to curve forward and ventralward 

 toward the uncus. The greater mass of the fibres coursing in the fornix arise as 

 outgrowths of the cells of the uncus, hippocampal gyrus, and dentate gyrus. They 

 accumulate as a dense stratum on the ventricular surface of these gj^ri, termed the 

 alveus, which crops outward as the fimbria and which passes backward and up- 

 ward; upon reaching the region of the splenium it turns obliquely forward under 



Fig. 682. — Diagram Showing Fornix and its Connections as seen from Above. 



Olfactory bulb ■ 



Medial olfactory stria 

 Subcallosal gyrus 

 Column (anterior pillar) 



Fimbria 



Mammillo-thalamic fasciculus 

 Stria terminalis of thalamus 



Stria medullaris of thalamus 

 Crus (posterior pillar) 



Epiphysis (below) 



Digitations (pes) of the 

 hippocampus 



Amygdaloid nucleus 



— Hippocampus major 



Hippocampal commissure (lyra) 



it and approaches the mid-line, to fuse with the like bundle from the gyri of the 

 hippocampus of the opposite side. The bundles thus arising from the two sides 

 are the pillars or crura of the fornix. They appear as two flattened bands of white 

 substance which come in close contact with and even adhere to the splenium. 



The angle formed by the mutual approach of the posterior piUars of the fornix is crossed 

 by a lamina of commissural fibres connecting the hippocampal gyri of the two hemispheres 

 (fig. 68-4). This lamina is the hippocampal commissure or transverse Jornix. Like those of the 

 fornix, its fibres arise from the cortex of the hippocampal gyri, but they serve as commissural 

 fibres between the hippocampal gyri of the two hemispheres. Being of a different functional 

 direction, it should not be considered a part of the fornix. The angle formed by the two pos- 



FiG. 683. — Diagram Illustrating the Origin and Course of Fornix as viewed from the 



Side. 



Gyrus cinguli 

 Cingulum 



Longitudinal striae 

 Fornix 



Olfactory bulb and tract 



Anterior perforated substance 

 Uncus - 



Perforating fibres 



_ Thalamic medullary stria 

 . Habenular nucleus 



Mammillo-thalamic 

 fasciculus 



•Longitudinal strise 

 ■Calcarine fissure 



Mammillo-mesencephalic 

 fasciculus 



^Fimbria 

 Hippocampal gyrus 



Mammillary body 



terior pillars of the fornix as traversed by the hippocampal commissure gives a picture named the 

 psalterium or lyra. Usually the hippocampal commissure and the posterior pillars (crura) are 

 in close contact with the under surface of the splenium. When occasionally they do not adhere, 

 the space between is known as Verga's ventricle. According to recent studies of brains with 

 degenerated corpus callosum, further commissural fibres between the limbic lobes course in the 

 posterior angle of the septum pellucidum, and all along, transverse to the body of the fornix. 



The body of the fornix appears as a triangular plate of white substance 

 produced by the fusion of the pillars. Its base or widest portion is behind. It 

 is not always bilaterally symmetrical. Its upper surface is attached hj the septum 



